The present invention relates to a method and a device for impregnating fibrous material, wherein by fibrous material, fibre bundles or strands, woven textiles or also fibre matting is understood, wherein in the latter case the individual fibres or filaments are present in a random orientation. The fibrous material can be made of the most varied materials; glass, carbon or aramid fibres can be used, or natural fibres such as, for example, flax, jute, hemp or cotton fibres, or metal fibres such as steel, copper or aluminium fibres, or plastics fibres such as, for example, polyethylene, polypropylene or polyamide, or polyethylene terephthalate fibres can be used. The soaking or impregnating of such fibrous materials is an important step in the manufacturing of fibre-reinforced composite substances, in which a good cohesion between a matrix substance and the fibres is vital. This good cohesion is only made possible by as complete as possible wetting of the surface of the individual fibres.
In particular, the present invention relates to a method for impregnating fibrous material, in which an impregnating agent is introduced into the spaces in the fibrous material, and the individual fibres are coated and/or soaked through, wherein the impregnating agent is supplied via a supply body with one or more apertures, on which body the fibrous material is moved past in contact with the supply body or at a distance from it.
The corresponding device for impregnating fibrous material, upon which the present invention is based, is provided with a supply body with one or more apertures for the impregnating material and transport means for the fibrous material, by means of which the fibrous is moved through the device, or respectively on the supply apertures or respectively moved past the supply body.
Such a method and a corresponding device are known from DE 38 35 574, whereby in this an impregnating device is described in which a fibre bundle is conveyed via a nozzle, wherein a plastics flux is pressed through the fibre bundle, at a raised pressure, at right-angles to the direction of movement of the fibres, which fibre bundle is consequently soaked through. With this, impregnation is carried out substantially locally by bringing together the fibrous material and a nozzle in one place, where, because of the pressure of the impregnating material leaving the nozzle, the fibre bundle, or respectively the fibrous material, is interspersed relatively quickly by the impregnating agent.
In comparison, a method and a device are also known in which the supply is by means of a permeable supporting surface moved at the same speed along with the fibrous material. Such a method and a corresponding device are relatively complex because of the supporting surface also having to be moved and the matching of the speeds of the fibrous material and the supporting surface.
The method and device with local supply, even when the local supply of impregnating material is repeated on a plurality of occasions in a succession of positions, have the disadvantage that the soaking through of the fibrous material is often irregular and incomplete. For example, in the case of fibre bundles, it can happen that the fibre bundles are of different thicknesses when seen from right-angles to their longitudinal extent, and because of this the impregnating material penetrating in this direction of thickness can encounter a very different flow resistance. The impregnating material then flows preferentially through areas with low flow resistance, in certain conditions even separating the fibre bundle in this way, and only poorly soaks through the thicker areas of the bundle.
JP 984615 shows a device with a tube-shaped base body. A slit extending in a longitudinal direction is arranged in this tube-shaped base body. A sintered body is incorporated into this slit, through which sintered body the impregnating agent is supplied to the fibres.
Compared to this prior art, the object of the present invention is to provide a method and a device which achieve a more complete and uniform soaking through of the fibrous material.
With respect to the method, this object is solved in that a supply body of a permeable or porous material is used for the supply of the impregnating agent, over which body the fibrous material is moved along in a sliding manner.
Preferably, the permeable or respectively porous supply body has, when seen in the direction of flow of the impregnating material, a greater flow resistance than the fibrous material. It is clear that the flow resistance of the fibrous material is to be viewed as the same direction as that in which the impregnating material is pressed through the fibrous material, that is to say perpendicular to the contact surface of the permeable or respectively porous supply body.
A configuration of the method is preferred in which the supply of the impregnating agent is done under moderate pressure of, for example, at least 10 and at the most 500 bar in the case of thermoplastic impregnating agents, and 1 to 50 bar with duroplastic impregnating agents, measured on the side of the porous supply body opposite the fibrous material.
Furthermore, a configuration of the method according to the invention is preferred in which the dimensions of the supply body, that is to say in particular its porous surface, over which the fibrous material is passed, and the speed of movement of the fibrous material which is to be soaked through are matched with one another such that a given point of the fibrous material which is touching the contact surface of the supply body, remains touching this contact surface for at least 50 milliseconds (ms), thus actually requires at least 50 ms to be moved over the length of the contact surface, measured in the direction of movement of the fibrous material. In other words, when the fibrous material moves relative to the supply body at a speed of 50 mm per second, the length of the contact surface of the porous supply body would have to be at least 2.5 mm, and if the speed of the fibrous material is 500 mm per second, the corresponding length of the supply body would have to be 25 mm.
With the aid of the method according to the invention, duromer impregnating agents can be applied to fibres without any problems, which agents are then cured after impregnation of the fibres. Unexpectedly, it has been proved that even thermoplastic materials which have a substantially greater viscosity compared to duromers, can be applied very well through permeable or respectively porous supply bodies which have relatively small effective cross-section supply apertures, and possibly also relatively long supply channels to the fibres to be impregnated using the method according to the invention. Moreover, it has been established that the speed at which the fibrous material can move relative to the supply body can be increased substantially above the figures already described, as in many cases a contact time of 10 milliseconds is enough for sufficiently wetting the fibrous material to be impregnated or soaked through. The supply body can either be correspondingly shortened or the speed of supply of the fibrous material can be correspondingly increased, for example, to 1-5 m per second.
A particular application of the method according to the invention is disclosed in connection with the application of the impregnated fibres onto blank moulds. These can be, for example, rod or tube-shaped and the fibres can either be applied in the longitudinal direction of such a blank mould or be wound around it, at an angle which can in principle, be selected between 0xc2x0 (corresponding to the longitudinal direction) and 90xc2x0 (corresponding to wrapping in a plane perpendicular to the feed direction of the blank mould).
The blank mould can either be rotated or the supply means for the fibres is rotated together with a corresponding impregnating means around the blank mould, according to which variant proves more practically advantageous. In particular when the blank moulds are of a very great length, for example in the case of relatively long pipelines, it is often advantageous to arrange the impregnating and fibre supply means to be rotatable about the blank mould when it has to be wound with impregnated fibrous material. With shorter blank moulds such as, for example, short pipe sections or squares, the opposite method, of rotating the blank mould, is possibly more advantageous.
With other variants of the method according to the invention, the fibrous material is conducted through the inside of a hollow body which can admit the impregnating agent, wherein the hollow body is composed of the porous or respectively permeable material described.
The fibres can be conducted through a plurality of successive hollow bodies, in a multi-stage process, wherein at each hollow body a further, new fibre layer is applied and supplied to the existing impregnated fibre layer, which new layer is impregnated when passing through the respective next hollow body.
When wrapping, in particular a plurality of different groups of fibres can be wound simultaneously onto a blank mould, wherein by means of this method, either a larger winding width is obtained, so that the feed speed of the blank mould can be increased, or a plurality of layers of fibres can be wound one on top of another directly one after another. Clearly, the groups of fibres can also have, respectively, different fibrous materials.
A winding or applicator device is advantageously followed by an appropriate means, which in the case of duromer impregnating agents can be generally a heating means, an irradiating means or the like, for curing the duromer material, while in the case of a thermoplastic material only wiping, post-forming and cooling down takes place.
With respect to the device, the object of the invention is solved in that the supply body is composed of a substantially homogeneous, porous and respectively permeable body, wherein the porous body is provided such that it comes into contact with the fibrous material. Preferably, the flow resistance of the supply body for the impregnating material is greater than the flow resistance of the fibrous material perpendicular to the contact surface of the supply body. A substantially homogeneous, porous pr respectively permeable body is understood to be a supply body, the material of which continuously has the same chemical and physical properties, that is to say in every instance when viewed from areas which are clearly larger than the pores or apertures in the material. Advantageously, the apertures or pore sizes in the material of the supply body should also be distributed as homogeneously as possible and be of the same size, that is to say the size distribution of the individual pores should have only a slight degree of variation. Additionally, such a porous material should naturally be open-pored, thus allowing the desired permeability. For example, the supply body can be composed of a sintered material which is manufactured by sintering together a granulate material, preferably with a particle size of less than 1 mm. The average aperture size of the individual pores should be preferably not exceed 0.2 mm in diameter, wherein this optionally also allows the use of a sinter material with correspondingly finer particles.
Instead of a porous material or sintered material, the permeable or respectively porous supply body could also be made, for example, from a plurality of layers of a sufficiently dense woven textile or mesh, which is preferably manufactured from individual filaments which are advantageously scarcely wettable with the impregnating material. A perforated plate or the like could also be provided. Such a perforated plate could be produced by means of many fine bores in a material such as metal, ceramic or plastics. The diameter of the bore in this case is preferably between 1 and 5000 xcexcm, preferably between 10 and 1000 xcexcm, and their distance apart from one another is approximately 1 to 1000 xcexcm. The preferred ratio of length to diameter of the bores is between 0.05-2000, preferably between 0.1 and 1000, in particular between 0.5 and 100.
Additionally, the supply body should preferably be composed of a material to which the impregnating agent adheres only with difficulty, or which is chemically resistant to solvents for the impregnating material.
It can also be advantageous when the contact surface of the supply body is intentionally configured as a surface with a low degree of sliding friction for the fibrous material. For example, the surface of the porous body which comes into contact with the fibrous material could be polished. This surface could also be selectively coated with a suitable slip material and, for example, be galvanised in order to reduce the friction between the fibrous material and the surface of the porous supply body. In many cases, however, the more or less abrasive fibrous materials ensure that an initially rough surface of a sintered body or other permeable body, is xe2x80x9cgroundxe2x80x9d or respectively polished after a relatively short period of time.
The thickness of the porous supply body should be great compared to the thickness of the fibrous material to be soaked through, and be at least double the latter, in each case measured in the direction of flow of the impregnating material, so that the substantial pressure loss along the porous body occurs, and the wetting front in the fibrous material proceeds as regularly as possible throughout the thickness of the fibrous material, even when the fibres in the fibrous material are arranged with different density.
The corresponding device separately has the means which are necessary for carrying out the method steps described hereinabove. One of the variants of the device according to the invention is in the configuration of a porous and respectively permeable supply body as a hollow body, wherein the fibres are conducted through the inside of this hollow body and the impregnating agent is applied to the hollow body from the outside, which agent penetrates the wall of the hollow body into the inside. Advantageously, the intake area of such a substantially cylindrical or otherwise contoured hollow body is configured as convex in the direction in which the fibres run, that is to say as a more or less funnel-shaped or trumpet-shaped intake area.
In order to apply the fibrous material to a blank mould, in a preferred variant of the invention, a holder is provided for the blank mould, which is moveable relative to an impregnating means along an axis. In this way the impregnated fibres can be applied to the blank mould in the longitudinal direction. When the blank mould is simultaneously rotated, for which, in a corresponding embodiment an appropriate rotating means is provided, the fibres are wound onto the blank mould, at an angle relative to the direction of advancement of the blank mould, the tangent of which corresponds to the relationship of the speed of rotation at the periphery of the blank mould to the speed of advancement, and which is therefore substantially adjustable between 0xc2x0 and 90xc2x0. Instead of rotating the blank mould, which can cause difficulties under some conditions with very long blank moulds, which are manufactured in principle as endless material, a winding device can also be provided by means of which a fibre supply means is arranged to rotate with the corresponding impregnating means around the blank mould.
A plurality of fibre supply means can also be provided to rotate independently of one another or together with one another around the blank mould. Independently rotatable fibre supply means allow different layers of fibres to be applied to the blank mould at different angles relative to the direction of advancement. A plurality of fibre supply means can each have their own impregnating means which is rotatable together with the supply means; optionally, however, a common impregnating means can be provided when the fibre supply means rotate together and the impregnating device is also provided to rotate correspondingly.
In the preferred embodiment, the porous and respectively permeable body is a sintered material manufactured from a sinter powder with a particle size in the range between 0.1 and 1000 xcexcm, preferably in the range between 10 and 500 xcexcm. The thickness of such a porous sintered body should be, in the preferred embodiment of the invention, at least 1 mm, preferably 2, and particularly preferably more than 5 mm. This produces effective supply channels through the porous sintered body, the ratio of length to diameter of which (wherein this is based on an average diameter of the channels) is in the size order of 10 to 1000. The exact ratio of length to diameter and also the absolute average diameter of the supply channels depends very greatly upon the impregnating agent, wherein very viscous materials tend to form a larger free supply cross-section through the individual channels. In particular, a permeable body could also be manufactured, for example, in which an appropriate metal plate or otherwise shaped supply body could be provided with very fine bores of less than 1 mm diameter with the aid of a laser, for example with bores of 0.2 to 05 mm diameter. Several meshes, gratings or woven textiles of metal or other materials could also be used as porous, permeable supply bodies.
It has been unexpectedly proved that porous sintered bodies manufactured from sinter grains with an average diameter of less than 500 xcexcm are also extremely suitable for impregnating using thermoplastic materials, even when the effective supply channels have a ratio of length to diameter in the size order of 100. This is probably because, inter alia, these highly viscous, thermoplastic materials are as a rule non-Newtonian liquids, that is to say their viscosity changes with the respective flow conditions, and can even reduce at high relative speeds.
According to the basic concept of the invention, a fibrous material, that is to say one or more bundles of fibres or respectively a woven textile or also a fibre mat, is conducted over a permeable or porous material or respectively a permeable or porous body. The fibres and the porous body are in contact with one another, wherein this can be achieved either by applying an opposing body, for example a press roller or a press shoe, or by producing a suitable tension in the fibrous material and by suitable shaping of the porous body and corresponding guiding of the fibrous material. A fluid or respectively a flux is fed through the porous body. At the place where the flux or respectively the fluid emerges, where the fibrous material is in contact with the porous body, the flux or respectively the fluid directly penetrates the fibrous material and soaking through takes place. In contrast to the prior art, the soaking though or respectively impregnation takes place continuously during the entire time the material is running over the surface of the porous body. At the same time, a relative movement between the fibrous material and the porous body takes place. The method according to the invention and the corresponding device are not only suitable for low viscosity fluids or fluxes, but can also be satisfactorily configured for higher viscosity materials in that, for example, the supply pressure is increased and/or the permeability and if necessary the pore size of the porous or respectively permeable body is increased. With respect to the manner of functioning of the present invention, the relatively long contact time of the fluid or respectively flux emerging continuously at a slight pressure and the fibrous material appears in particular to be positive, and the fibrous material can, in this way, be very uniformly soaked through.
Naturally, different features of the embodiments described, and yet to be described, are independent of one another, and can also be used with methods and a device not using a supply body with a large number of small apertures. This is the case, for example, for the winding device to be described in more detail hereinafter, the supply of impregnating agent in a hollow body from the outside to the inside, and other features which are recognisable to the skilled person as independent from the special supply body.
Further advantages, features and possibilities for application of the present invention will be evident from the following description of a preferred embodiment and of the attached drawings. There is shown, in: